Assessment of the visual quality of ornamental plants:
comparison of three methodologies in the case of the
rosebush
Pierre Santagostini, Sabine Demotes-Mainard, Lydie Huché-Thélier, Nathalie
Leduc, Jessica Bertheloot, Vincent Guérin, Julie Bourbeillon, Soulaiman Sakr,
Rachid Boumaza
To cite this version:
Pierre Santagostini, Sabine Demotes-Mainard, Lydie Huché-Thélier, Nathalie Leduc, Jessica
Bertheloot, et al.. Assessment of the visual quality of ornamental plants: comparison of three
methodologies in the case of the rosebush. Scientia Horticulturae, Elsevier, 2014, 168, pp.17-26.
.
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1
Assessment
2
methodologies in the case of the rosebush
of the visual quality
of ornamental
plants:
comparison
of three
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a
b
b
c
b
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P. Santagostini , S. Demotes-Mainard , L. Huché-Thélier , N. Leduc , J. Bertheloot , V.
5
Guérin , J. Bourbeillon , S. Sakr and R. Boumaza
b
d
d
d,*
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a
Agrocampus Ouest, F-49045 Angers cedex, France
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b
INRA, UMR1345 IRHS (Institut de Recherche en Horticulture et Semences), SFR 4207
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QUASAV, F-49071 Beaucouzé, France
c
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Université d’Angers, UMR1345 IRHS, SFR 4207 QUASAV, PRES L’UNAM, F-49045
Angers, France
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d
Agrocampus Ouest, UMR1345 IRHS , SFR 4207 QUASAV, F-49045 Angers, France
13
*
Corresponding author: Rachid Boumaza, Agrocampus Ouest, 2 rue A. Le Nôtre, F-49045
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Angers cedex, France
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E-mail adresses
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[email protected]
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[email protected]
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[email protected]
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[email protected]
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[email protected]
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[email protected]
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[email protected]
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[email protected]
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[email protected]
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ABSTRACT
The quality of ornamental plants can be appraised with several types of criteria: tolerance
29
to biotic and abiotic stresses, development potentialities and aesthetics. This last criterion,
30
aesthetic quality, is specific to ornamental plants and objective measurements are required.
31
Three methodologies for measuring aesthetic quality have been proposed. The first involves
32
classical measurements of morphological features, such as flower number and diameter or leaf
33
size. The second is based on sensory methods recently adapted to ornamental plants. The
34
third, used by the International Union for the Protection of New Varieties of Plants (UPOV)
35
for distinctness, uniformity and stability (DUS) tests, is based on morphological
36
characteristics calibrated on specific reference varieties. The aim of this work was to compare
37
these three methodologies for assessing some flowering and foliage characteristics of
38
rosebushes. Six plants from 10 rose varieties identified by UPOV as reference varieties were
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cultivated for two years in a greenhouse and outdoors in Angers, France. They were measured
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and photographed weekly during flowering. Photographs of the plants in full bloom were
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submitted to a panel of judges for sensory assessment. The results of the three assessment
42
methodologies were compared. Sensory and morphometric measurements were highly
43
correlated and sensory measurements confirmed UPOV scales, whereas some morphometric
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measures diverged slightly from UPOV scales. We discuss the advantages, disadvantages and
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complementarity of these three methodologies.
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Keywords
UPOV; rose; aesthetic quality; sensory analysis; floribundity.
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Abbreviations
UPOV: International Union for the Protection of New Varieties of Plants
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1 Introduction
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Quality is defined by the ISO 8402-1986 standard as “the totality of features and
56
characteristics of a product or service that bears its ability to satisfy stated or implied needs”.
57
The quality of plants can be appraised with several types of criteria: tolerance to biotic and
58
abiotic stresses, development potential and aesthetics, a criterion specific to ornamental plants
59
(Habib et al., 1997; Dijkshoorn-Dekker, 2002; Heuvelink et al., 2004, Giorgioni, 2007). The
60
measurement of aesthetic quality is necessary for objective studies, such as modelling or
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assessing the effects of various treatments. However, as pointed out by Boumaza et al. (2009),
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the multiple possibilities make it difficult to measure.
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The characteristics of aesthetic quality to be taken into account depend on the type of
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ornamental plant considered: trees, shrubs, bushes or cut flowers. However, some of these
65
characteristics may be common to several plant categories. We focus here on the rosebush, a
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model plant in ornamental horticulture, considering only visual aspects and ignoring all
67
considerations relating to scent. Furthermore, we do not aim to characterise the visual quality
68
of all the aerial parts of the plant. Indeed, this aspect has been dealt with in previous studies
69
based on the use of tools and methods from the domain of sensory analysis (Boumaza
70
2010, Huché-Thélier et al., 2011) or architecture analysis (Morel et al., 2009, Crespel et al.,
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2013). Instead, we focus on the partial evaluation of flowers and leaves, two of the principal
72
determinants of the visual quality of the rosebush.
et al.,
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Floribundity is defined as “the capacity of a plant to produce abundant flowers at high
74
density on each of its branches” (http://fr.wiktionary.org/, 10/11/2012). However, should we
3
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take into account the number of flowers at peak flowering or throughout the year? In its
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guidelines, UPOV specifies that all observations should be made when the plant is in full
77
flower (UPOV, 2010). Hereafter, we refer to this measurement as the peak floribundity index.
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The longitudinal floribundity index is the variation of the floribundity index during a season.
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Another related question concerns the stage at which flowers should be counted. Should we
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count all flowers, regardless of their stage of development (buds, opened, withered, rose hips)
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or only fully opened flowers? If we focus on the vitality of the plant, it would be tempting to
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consider all the flowers. However, if we are more concerned about visual quality, we may
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wish to restrict the flower count to opened flowers – that is, flowers with visible petals – and
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rosehips. Indeed, these two types of organ are brightly coloured and stand out from the foliage
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of the rosebush, which is usually green once the leaves have fully emerged. The peak
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floribundity index reported here takes into account all flowers but not the rosehips, whereas
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the longitudinal floribundity index takes only open flowers into account. We characterised
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floribundity by three types of methods or methodologies: the morphometric methodology, the
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sensory methodology and the UPOV methodology. The flower and leaf dimensions were
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characterised by the morphometric and UPOV methodologies.
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The morphometric methodology is classically used in agronomy. It includes all methods
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based on counting, such as flower, leaf or axis counts, methods based on the measurement of
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dimensions, such as the diameters and heights of flowers, the lengths and widths of leaflets
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and stem length, and methods based on image analysis.
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The sensory methodology involves the methods and tools initially used in sensory
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analysis. These methods were originally developed in the agro-food industry and have since
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been extended to other domains. They have recently been adapted for the objective
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characterisation of the visual quality of ornamental plants, as perceived by the human eye,
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which can be considered as a measurement instrument in this context (Boumaza et al., 2009).
4
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These methods require the choice of appropriate descriptors, the constitution of a jury of
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about 15 judges and the evaluation of each descriptor for each product. Two applications
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(Boumaza et al., 2010; Huché-Thélier et al., 2011) have demonstrated the relevance of such
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methods to ornamental horticulture, a sector in which visual quality is an important
104
component of the commercial value of the products.
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The UPOV methodology is based on the DUS (distinctness, uniformity and stability)
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requirements laid down by UPOV in 1990 for the examination of cultivars or varieties for the
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acquisition of plant breeders’ rights. This method is based on scoring rosebushes on a scale of
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1 to 9 for characters identified as useful for distinguishing between varieties or for evaluating
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the uniformity and stability of a variety. Scores of 1, 3, 5, 7 and 9 correspond to examples of
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varieties that will be referred hereafter as reference varieties (Table 1). The most important
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feature of this method is that the relative behaviour of the reference varieties is identical in all
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environments. In some ways, this renders this approach almost international. In this study, we
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also considered the relevance of this approach, although this was not the principal objective.
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The reference varieties studied here were those used between 1990 and 2010. The
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recommendations for the DUS examination were subsequently modified in 2010 (UPOV,
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2010). This modification led to changes in the reference varieties for the two characters
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considered. However, this does not undermine the importance of this work, which was begun
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in 2008 and focuses on a key question: Is it possible to decrease the costs of rosebush
119
evaluation when using a sensory method, and if so, how? Indeed, if the requirements for the
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reproducibility and repeatability of measurements are to be respected, the sensory method is
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more expensive than morphometric analyses. Furthermore, neither of these two methods has
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the almost international nature of the UPOV method.
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The aim of this study was, therefore, to compare these three methodologies. We evaluated
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floribundity, and the flower and leaf dimensions of UPOV reference roses, and then compared
5
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the results obtained and considered the advantages and disadvantages of each methodology.
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For validation of some of the findings of these comparisons, we also considered the data
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obtained for rosebushes by Boumaza et al. (2010), referred to hereafter as supplementary
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data.
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2 Materials and Methods
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2.1. Plant material and growing conditions
133
Ten rosebush varieties, listed in Table 1, were cultivated at Angers, France (latitude:
134
47° 30’ N; longitude: 0° 35’ W; altitude: 56 m). The rosebushes were grafted onto Rosa
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corymbifera ‘Laxa’, except for the ‘Sweet Promise’ variety, which was grafted onto Rosa
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canina ‘Schmids Ideal’. Experiments were conducted in a greenhouse from November 2008
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to April 2010 and outdoors from April 2010 to September 2011.
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2.1.1. Growing conditions in the greenhouse
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In November 2008, 60 rosebushes (6 per variety) were planted in 7-litre pots, in a
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substrate composed of peat, coconut fibre and perlite (60/30/10, v/v/v). The pots were
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randomly placed on a shelf in six rows, 0.75 m apart and then pruned. The plants were drip
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fertiirrigated with a liquid fertiliser (Servital®, with a 3–2–6–0.6 balance of N–P
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MgO, a pH of 5.8 and a mean electrical conductivity (EC) of 1.8 mS cm
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of water, which was 0.3 mS cm ). Each plant received between 330 mL of solution every two
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days in winter and 1330 mL per day in summer. Pests and diseases were controlled.
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Additional lighting (60 µmol m
149
sodium vapour lamps when total radiation levels outside the greenhouse fell below 200 W m
-1
2O5–K2O–
, including the EC
-1
−2 −1
s of photosynthetically active radiation) was provided by
6
-
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2
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approximately to the measurement period, mean diurnal temperature was 25.6 °C (minimum:
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18.4 °C and maximum: 45.0 °C) and mean humidity was 48% (minimum: 15% and
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maximum: 85%).
. Daylength was extended to 16 h. From March to September 2009, corresponding
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155
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2.1.2. Outdoor growing conditions
In mid-April 2010, the 53 surviving rosebushes (7 had died) were transferred outside,
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together with new rosebushes to replace those that had died, to obtain six replicates per
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variety. They were planted randomly in six blocks, 2 m apart, on a silty clay soil covered by a
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porous plastic mulching film. They were drip irrigated with 500 mL of water per plant every
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non-rainy day, from April to September. Pests and diseases were controlled. From mid-April
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to September 2010, corresponding approximately to the measurement period for 2010, mean
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diurnal temperature was 19.5 °C (minimum: 3.1 °C; maximum: 36.7 °C) and total rainfall was
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156 mm. During the 2011 measurement period, corresponding approximately from April to
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September, mean diurnal temperature was 19.1 °C (minimum: 6.2 °C; maximum: 35.9 °C)
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and total rainfall was 230 mm.
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2.2. Morphometric measurements
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2.2.1. Leaves
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Measurements were made on the UPOV reference varieties for leaf dimension: ‘Tancary’,
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‘Mullard Jubilee’, ‘Kolima’, ‘New Daily Mail’, ‘Starina’ and ‘Meiblam’, from 12 April to 10
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August 2009 in the greenhouse and from 3 May to 10 August 2010 outdoors. The length of
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the rachis, and the length and width of all leaflets of the leaves located in the central third of
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each flowering shoot were measured when the terminal flower carried by this shoot withered.
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As reported for the ‘Radrazz’ variety by Demotes-Mainard et al. (2009), the length of the
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terminal leaflet was correlated with all the other leaf measurements taken, regardless of the
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variety considered. We therefore chose to use this character for comparisons of leaf
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dimensions.
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2.2.2. Flowers
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Measurements of flower diameter were made on the UPOV reference varieties:
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‘Meichim’, ‘Pink Wonder’, ‘Kolima’, ‘Sweet Promise’, ‘Starina’ and ‘Meiburenac’, from 3
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April to 2 September 2009 in the greenhouse and from 8 April to 29 September 2010
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outdoors. We measured the diameter and height of almost all the flowers at anther dehiscence
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during the first flush of flowering (ending in mid-July).
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The numbers of flowers (buds, open and withered flowers) were counted on the
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rosebushes of the UPOV reference varieties for flower number (‘Meichim’, ‘Kolima’, ‘Sweet
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Promise’ and ‘Meiburenac’) during the first flowering period, on days determined according
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to plant development, generally when withered flowers were observed on the rosebush.
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Almost all the replicates of the varieties used for floribundity measurements in the greenhouse
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(in 2009) and a single rosebush per variety outside (in 2010 and 2011), were photographed,
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about once per week. The relative flower area, that is the ratio of the area covered by flowers
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to that covered by the entire plant (Figure 1), was determined with ImageJ (Rasband, 2011).
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This ratio and the number of flowers were considered as floribundity indices.
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2.3. Sensory measurements
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These measurements were carried out on the reference varieties ‘Meichim’, ‘Kolima’,
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‘Sweet Promise’ and ‘Meiburenac’. One field-grown plant per variety was photographed
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about once weekly, and we selected three photographs for each plant, some of which were
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taken at peak flowering. We trained a jury of 16 assessors, to ensure that they interpreted the
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overall level of flowering in the same way, and established a structured nine-level scale with
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three photographs for each odd-numbered level (Figure 2). The photographs used for training
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purposes were, of course, different from those subsequently used for assessment. After the
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training session, the assessors were asked, individually, (i) to sort the 12 chosen photos into
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ascending order of flower quantity, taking into account buds and withered flowers, (ii) to sort
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them according to the relative area occupied by the open flowers, that is the ratio of coloured
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flower area to total plant area, (iii) to score the level of flowering on the nine-level scale they
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had previously established (Figure 2). Each assessor carried out three scoring sessions, at one-
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week intervals.
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2.4. Supplementary data
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As part of the sensory evaluation carried out by Boumaza et al. (2010), 10 rosebush
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photographs (Fig. 3) were evaluated by 14 judges in three sessions. The judges provided
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scores for some descriptors, three of which were related to floribundity: “Number of flowers”,
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“Flower enhancement” and “Number of buds”. These scores were used to rank the 10
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rosebushes for each descriptor/session/judge. Then, for each descriptor, we averaged the 42
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ranks of each rosebush to get a mean rank per rosebush/descriptor. The relative flower area of
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each rosebush was measured independently, with the image analysis method described in
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section 2.3. All these data are reported in the table associated with figure 3.
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2.5. Statistical analyses
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All statistical analyses were carried out in the R environment (R Development Core Team,
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2011), with the stats, graphics and agricolae packages. Analysis of variance was used for
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variety comparisons. When the conditions for the application of this method were not
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fulfilled, nonparametric tests (Kruskal-Wallis or Friedman test) were used (Conover, 1999).
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3 Results
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3.1. Leaf dimensions
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Both in the greenhouse and outdoors, the ranking of varieties (Table 2) matched that of
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the UPOV scale (Table 1), except for ‘Mullard Jubilee’, the level 7 (large leaves) reference
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variety. It was not possible to distinguish this variety from the ‘Tancary’ and ‘New Daily
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Mail’ varieties, level 9 (very large leaves) reference varieties on the basis of our
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morphometric measurements. We were therefore able to construct a four-level scale for leaf
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dimensions, with specific reference varieties: “very small” with ‘Meiblam’, “small” with
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‘Starina’, “medium” with ‘Kolima’ and “large or very large” with ‘Mullard Jubilee’, ‘New
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Daily Mail’ and ‘Tancary’.
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3.2. Flower dimensions
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The diameters of the terminal flowers were found to be significantly greater than those of
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the other flowers for the ‘Starina’ and ‘Meiburenac’ varieties. We therefore excluded the
248
terminal flowers of plants of these two varieties from the calculations of mean diameter, as
10
249
recommended by UPOV (1990). By contrast, for ‘Pink Wonder’, we found no difference
250
between the diameters of terminal and non-terminal flowers, and the difference between these
251
two types of flowers was very small for ‘Kolima’. Hence, as fewer data were available for
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these two varieties, we considered all the flowers, both terminal and non-terminal, in the
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calculation of mean flower diameter.
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The mean flower diameters for each variety (Table 3), obtained in two consecutive years
255
in very different growing conditions (one year in the greenhouse and the second year
256
outdoors), were of the same order of magnitude. The largest difference was that for ‘Kolima’,
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which produced flowers with a mean diameter of 74 mm in the greenhouse and 83 mm
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outdoors. Pairwise comparisons of rosebushes growing outside led to the identification of two
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groups. The first consisted of the varieties ‘Starina’ and ‘Meiburenac’, the reference varieties
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for level 1 (very small) and level 3 (small), respectively, on the UPOV scale (Table 1). The
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second group consisted of the varieties ‘Kolima’ and ‘Pink Wonder’, the reference varieties
262
for level 5 (medium-sized) and level 7 (large), respectively. Three groups were identified in
263
greenhouse conditions: the first consisted of ‘Starina’ and ‘Meiburenac’, the second of
264
‘Kolima’ and the third of ‘Pink Wonder’.
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Thus, flower diameter measurements did not discriminate between reference varieties with
266
very small and small flowers either in the greenhouse or outdoors, or between reference
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varieties with medium-sized or large flowers outdoors. It was therefore possible to construct a
268
two-level scale for rosebush flower diameter from morphometric measurements: very small or
269
small flowers, with ‘Starina’ and ‘Meiburenac’ as the reference varieties, and medium-sized
270
or large flowers, with ‘Kolima’ and ‘Pink Wonder’ as the reference varieties. This scale partly
271
confirms the UPOV scale but, with only two levels, it is not suitable for use in practice.
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3.3. Floribundity
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3.3.1. Number of flowers
When we considered the number of flowers during the first full flowering of each plant,
277
the ranking of the varieties (Table 4) did not perfectly match the UPOV classification (Table
278
1). Indeed, our measurements suggest that ‘Meiburenac’ is a highly floriferous variety (105
279
flowers/plant in the greenhouse and 213 flowers/plant outdoors), followed at some distance
280
by ‘Kolima’ (24 and 33 flowers/plant, respectively). ‘Sweet Promise’ systematically produced
281
fewer flowers (15 and 17 flowers/plant, respectively) than these two varieties. However,
282
‘Meichim’, the least floriferous variety according to UPOV, behaved inconsistently,
283
producing a similar number of flowers to Sweet Promise in the greenhouse (12 flowers/plant),
284
but a number of flowers between the values obtained for ‘Kolima’ and ‘Sweet Promise’
285
outdoors (23 flowers/plant).
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3.3.2. Sensory data
When dealing with sensory data, the first step is the use of several techniques to evaluate
289
jury repeatability and reproducibility (Dijksterhuis, 1995, Rossi, 2001). The detailed results of
290
this process are not shown. From the analysis of sensory data through studies of the
291
distribution of ranks or scores, we noted that the consensus between the judges was best for
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classification by number of flowers and slightly weaker for scores of flowering level and for
293
classification by the ratio of flower area to total plant area, but the use of these results did not
294
affect the principal findings for variety classification.
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For each of the three previous sensory evaluation tests (classification by number of
296
flowers, area of the photograph covered by flowers and scores for flowering level),
297
comparisons of varieties gave identical results (Table 5), confirming the UPOV classification
12
298
for the number of flowers per flowering branch: few (with ‘Meichim’ as the reference
299
variety), medium (‘Sweet Promise’), many (‘Kolima’) and very many (‘Meiburenac’). Thus,
300
the perception of floribundity by the human eye is entirely consistent with UPOV
301
measurements.
302
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3.3.3. Morphological measurements and their relationship to sensory data
304
For the 12 photographs of rosebushes used for sensory evaluation, we determined the
305
coefficients of correlation between the relative flower area, the number of flowers counted in
306
the field and the mean scores provided by the jury (Table 6). These correlations were found to
307
be strong. This
308
floribundity, as perceived by the human eye, can be assessed simply from a photograph. We
309
will consider this aspect further.
finding opens up interesting
new possibilities, in that it suggests that
310
311
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3.3.4. Longitudinal floribundity
In the previous sections, only the instantaneous measurements of floribundity were
313
considered, in analyses of measurements corresponding to peak flowering. So, what about the
314
longitudinal floribundity (i.e. changes in floribundity over time)?
315
For one rosebush per variety, we plotted changes in relative flower area and in number of
316
flowers over time (Fig. 4; graphs on the left). The two curves had the same shape, with peaks
317
occurring at approximately the same dates. Similarly, the times at which the area was null or
318
small corresponded to periods in which there were few, if any, flowers. The Spearman’s rank
319
correlation coefficients for the relationship between these two measurements were high
320
(Fig. 4; graphs on the right).
321
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If we consider the longitudinal floribundity obtained by counting the number of flowers
(Fig. 5), then ‘Meiburenac’ appeared to be much more floriferous than the other varieties.
13
323
Similarly, ‘Kolima’ produced more flowers at peak flowering than ‘Sweet Promise’ or
324
‘Meichim’, but this was not always the case for other rosebushes from the same varieties, as
325
some ‘Meichim’ rosebushes (not shown here) had larger numbers of flowers than ‘Kolima’
326
rosebushes in early autumn.
327
328
3.3.5. Supplementary data
329
330
Relative flower area was strongly correlated with the mean rank inferred from the
331
descriptor “Number of flowers” (Spearman’s rank correlation coefficient (R
S):
0.78, n = 10,
332
p = 0.01). It was not correlated with the mean rank inferred from the descriptors “Flower
333
enhancement” (RS = 0.45, p = 0.19) and “Number of buds” (RS = -0.14, p = 0.70).
334
335
4 Discussion
336
337
We used all three methodologies to assess floribundity, whereas only the UPOV and
338
morphometric methodologies were used to assess the dimensions of leaves and flowers. This
339
study focused on the choice of methodology for the simple assessment of these features in the
340
most universal and efficient manner possible.
341
342
4.1. Leaflet and flower dimensions: can we propose classes of values?
343
344
Based on the measurement protocol proposed by UPOV and specified in the materials and
345
methods section, the use of value classes, corresponding to the UPOV scores for terminal
346
leaflet length or flower diameter, would greatly simplify the evaluation of leaves or flowers
347
by the sensory methodology. We initially planned to define such classes on the basis of the
14
348
mean characteristics (terminal leaflet length and flower diameter) of the UPOV reference
349
classes. Despite the high degree of consistency of the mean characteristics obtained in
350
different growing conditions, the results obtained raise questions about this approach, in that
351
the varieties did not behave in the expected manner. The 1990 UPOV reference varieties do
352
not appear to be appropriate for the constitution of these classes, because there was
353
insufficient discrimination between the reference varieties, particularly for flower diameter.
354
Two alternative strategies are possible. The first would involve repeating the experiments
355
with the 2010 reference varieties (UPOV, 2010), checking that the relative behaviour of these
356
new reference varieties matched UPOV descriptions and determining whether these classes of
357
values could be considered valid for the Angers region. Given the cost of the experiment, an
358
alternative strategy, based on arbitrarily fixing five classes on the basis of the lengths or
359
diameters reported in tables 2 and 3, respectively, might be preferable. We chose to use the
360
same number of classes as the UPOV protocol: very small, small, medium, large, and very
361
large. For example, in outdoor conditions, the classes for terminal leaflet length could be
362
<25 mm (very small), 25-40 (small), 40-55 (medium), 55-70 (large), >70 mm (very large);
363
those for flower diameter could be <50 mm (very small), 50-65 (small), 65-75 (medium), 75-
364
90 (large), >90 mm (very large). These empirically and somewhat arbitrarily defined classes
365
have the advantage of simplicity and are suitable for use in the Angers region. However, they
366
are not valid for all conditions, because the upper limits of the very small and large classes
367
defining the limits of the three central classes, are not exactly the same in the greenhouse and
368
outdoors.
369
370
4.2. Which measurements best reflect the level of flowering of a rosebush?
371
15
372
Given the importance of flowering in ornamental plants, it would appear surprising that
373
UPOV considers only one flowering characteristic in its classification: the number of flowers
374
per flowering branch. Furthermore, the way in which this character should be assessed is not
375
specified in the UPOV guidelines, leaving plenty of room for differences in interpretation.
376
However, all the possible ways of assessing this character that we tested were sufficiently
377
highly correlated (Table 6), generating a consensus. Nevertheless, although the sensory
378
evaluations fully confirmed the UPOV scale, the morphometric measurements (number of
379
flowers and relative flower area) only partially confirmed the UPOV scale.
380
The main advantage of the sensory method is that it focuses on the consumer’s perception
381
of the plant. Furthermore, the scoring scale can be refined and adapted for the products that
382
the jury is asked to assess. However, it is cumbersome to implement and very time-
383
consuming, due to the requirement for jury recruitment and training, for example.
384
Morphometric methods are less subjective than sensory methods, although flower
385
counting may be tedious. By contrast, the relative flower area on a photograph proved to be a
386
suitable indicator of the level of flowering of the plant perceived by an observer. However,
387
this measurement does not match the definition of floribundity, in that two rosebushes may
388
have equivalent ratios but very different numbers of flowers. For example, figure 6 shows two
389
rosebushes: ‘Sweet Promise’ and ‘Meiburenac’, corresponding to the “medium” and “very
390
many” categories of the UPOV (1990) scale. Their peak flowering area ratios were 45%, with
391
30 flowers, for the ‘Sweet Promise’ rosebush and 47%, with 205 flowers, for the
392
‘Meiburenac’ rosebush. This problem can be alleviated, for example by dividing the ratio by
393
an estimate of the area of a flower from the corresponding variety. The advantage of this
394
approach is that the calculation of ratios from photographs can be automated, and this would
395
accelerate the analysis, provided that all the photographs analysed were taken in good lighting
396
conditions. This is a necessary condition to ensure that the colour of the flowers is reproduced
16
397
accurately on the photograph. Another advantage of this approach is that it is not necessary to
398
photograph the entire rosebush, as this measurement is a ratio that could be estimated on the
399
basis of a photograph of the heart of the rosebush alone. Image analysis would therefore be a
400
useful tool for estimating floribundity and changes in floribundity over time.
401
402
403
4.3. Is the relationship between the results of sensory methods and image analysis
confirmed?
404
405
The results obtained for the supplementary data highlighted the link between the
406
descriptor “Number of flowers” and relative flower area. They thus provide an additional
407
argument for using the relative flower area measured by image analysis as a possible
408
measurement of rosebush floribundity.
409
There was no link between the descriptor “Number of buds” and relative flower area. This
410
is not surprising as it no buds were visible on the photograph (if the petal colour was not
411
visible) or only a very small proportion of the area was covered by buds (when the petal
412
colour first became visible).
413
414
5 Conclusion
415
416
We compared the results of morphometric and UPOV methodologies for classifying
417
varieties on the basis of flower diameter and leaf dimension, and we identified several
418
discrepancies. We also compared these two methodologies with sensory methodology for
419
floribundity assessment. Our analysis highlighted a convergence of the results obtained with
420
the various methods and suggested that it should be possible to assess floribundity as
421
perceived by the human eye, by image analysis techniques. The main advantages of image
17
422
analysis methods over sensory methods are their rapidity and universal nature. Such methods,
423
which would be relatively simple to carry out, might prove very useful for quantitative and
424
objective measurements on large samples. This method would therefore be useful for studying
425
processes such as the progression of flowering, which is currently being studied in relation to
426
the genetic determinism of flowering (Kawamura et al., 2011) and is of interest to rose
427
breeders for the assessment of new cultivars.
428
429
Acknowledgements
430
431
We thank the experimental domain team (INEM) of Agrocampus Ouest, Angers, who took
432
great care of the roses, the people who helped us to take the photographs, all the judges who
433
assessed the rosebushes, Morgan Garbez who introduced us to the use of ImageJ software for
434
our image analyses and Michel Laffaire, recently retired, for his work and advice during the
435
three years of experimentation.
436
437
References
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characterization of the esthetic quality of the rosebush. J. Sens. Stud., 24, 774-796.
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Crespel, L., Sigogne, M., Donès, N., Relion, D., Morel, P., 2013. Identification of relevant
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Andrieu, B., 2009. Coordinated development of the architecture of the primary shoot in
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bush rose. In: B. Li, M. Jaeger, Y Guo (eds.). Plant Growth Modeling, Simulation,
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Visualization and Applications. IEEE Computer Society, pp. 214-221.
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Dijkshoorn-Dekker, M.W.C., 2002. Crop quality control system: A tool to control the visual
quality of pot plants. Thesis, Wageningen University, The Netherlands.
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Dijksterhuis, G. , 1995. Assessing panel consonance. Food Qual. Pref., 6, 7–14.
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Giorgioni, M.E.., 2007. Evaluation of Landscape Roses for Low-Maintenance Gardening.
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Acta Horticulturae, 751, 323-330.
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Habib, R., Triboï, E., Génard, M., & Le Bail, M., 1997. La nutrition azotée des cultures et la
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qualité des produits. In: Maîtrise de l’azote dans les agro-systèmes. Paris: INRA (Les
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colloques, no. 83). Reims (France), 19-20 novembre 1996.
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Heuvelink, E., Tijskens, P., Kang, M.Z., 2004. Modelling Product Quality in Horticulture: an
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Huché-Thélier, L., Boumaza, R., Demotes-Mainard, S., Canet, A., Symoneaux, R., Douillet,
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O., Guérin, V., 2011. Nitrogen deficiency increases basal branching and modifies the
465
visual quality of the rose bushes. Sc. Hort., 130, 325-334.
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Kawamura, K., Hibrand-Saint Oyant, L., Crespel, L., Thouroude, T., Lalanne, D., Foucher, F.,
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2011. Quantitative trait loci for flowering time and inflorescence architecture in rose.
468
Theor. Appl. Genet., 122, 661-675.
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470
Morel, P., Galopin, G., Donès, N., 2009. Using architectural analysis to compare the shape of
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471
472
473
Rasband, W.S., 2011. ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA,
http://imagej.nih.gov/ij/, 1997-2011.
R Development Core Team, 2011. R: A language and environment for statistical computing,
474
R Foundation for Statistical Computing, Vienna, Austria, 2011, ISBN 3-900051-07-0,
475
URL http://www.R-project.org.
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477
478
Rossi, F., 2001. Assessing sensory panelist performance using repeatability and
reproducibility measures. Food Qual. Pref., 12, 467–479.
UPOV, 1990. Guidelines for the Conduct of Tests for Distinctness, Homogeneity
and
479
Stability. Rose (Rosa L.), UPOV/TG/11/7, International Union for the Protection of New
480
Varieties of Plants, Geneva, Switzerland.
481
UPOV, 2010. Guidelines for the Conduct of Tests for Distinctness, Homogeneity
and
482
Stability. Rose (Rosa L.), UPOV/TG/11/8, International Union for the Protection of New
483
Varieties of Plants, Geneva, Switzerland.
20
484
Figure captions
485
486
Figure 1. Measurement of the relative flower area by the morphometric methodology, with
487
ImageJ software. The colour photograph (a) is first transformed into black and white (b) and
488
the proportion of the picture area covered by the plant is calculated (0.28). A threshold is then
489
set on the colour (here, red) to separate the flowers from the foliage (c), and the proportion of
490
the picture area covered by the flowers is calculated (0.12). The relative area of the plant
491
covered by the flowers is the ratio 0.12/0.28 = 0.45 in this case.
492
493
Figure 2. The structured nine-level scale established by the jury for the assessment of
494
floribundity by the sensory methodology. Each odd-numbered level is illustrated by three
495
examples.
496
497
Figure 3. Photographs of the 10 rosebushes (Boumaza et al., 2010) and the corresponding
498
data – used as supplementary data for validation. The numbers under each photograph
499
correspond to the relative flower area and the mean rank according to the sensory descriptors:
500
“Number of flowers”, “Flower enhancement” and “Number of floral buds”.
501
502
Figure 4. In the left column, for one plant (outdoors, 2010) per variety, we have plotted
503
changes in relative flower area (●) and in the number of open or withered flowers (▲) over
504
time. Time is shown on the x-axis (indicated by date). The left y-axis scale corresponds to
505
relative flower area and the right y-axis scale, to flower number. In the right column, the
506
relative flower area is plotted against the number of open or withered flowers, when these two
507
measurements were made on the same date. Rs denotes Spearman’s rank correlation
21
508
coefficient between the two measurements and n is the number of common date
509
measurements.
510
511
Figure 5. The number of open or withered flowers over time for one plant for each of the
512
varieties ‘Meiburenac’, ‘Kolima’, ‘Sweet Promise’ and ‘Meichim’.
513
514
Figure 6. Each photograph corresponds to the maximum ratio of areas shown on the
515
corresponding graph. For this ‘Meiburenac’ rosebush, the maximum was 45%, with 205 open
516
and withered flowers. For this ‘Sweet Promise’ rosebush, the maximum was 47%, with only
517
30 flowers.
22
Table(s)
1
Table 1. The reference varieties of the UPOV scales for the studied characteristics: flower
2
diameter, leaf size and number of flowers (UPOV, 1990).
Characteristics
UPOV score
1
3
5
7
9
Meiblam
Starina
Kolima
Mullard
– Tancary
Jubilee
– New Daily Mail
Pink
–
Leaf: size
Starina
Meiburenac
Kolima
Flower: diameter
a
Wonder
Flowering shoot:
number of
–
b
Meichim
Sweet
Kolima
Meiburenac
Promise
flowers
3
a
The variety Meinatac corresponding to a score of 9 was not found in the market.
4
b
A score of 1 has not been assigned to any variety.
5
21
6
Table 2. Leaf dimensions: average length (mm) and confidence interval (at 95% level) of the
7
terminal leaflet per variety. For each year, the letters indicate significant differences between
8
the varieties (LSD method, p < 5%).
Variety
2009, greenhouse
Number Mean
of plants
2010, outdoors
Confidence
Number Mean
interval
of plants
Confidence
interval
Tancary
6
79.9
[74.7 , 85.1]
a
6
72.8
[71.4 , 74.2]
a
New Daily Mail
6
80.3
[78.1 , 82.4]
a
6
71.1
[65.1 , 77.1]
a
Mullard Jubilee
3
83.7
[74.1 , 93.3]
a
6
67.5
[61.6 , 73.4]
a
Kolima
6
48.7
[45.5 , 52.0]
b
6
53.5
[48.7 , 58.4]
b
Starina
5
34.0
[32.7 , 35.2]
c
6
30.0
[26.8 , 33.3]
c
Meiblam
5
27.1
[24.5 , 29.7]
d
6
23.4
[20.2 , 26.5]
d
9
22
10
Table 3. Flower diameter (mm): mean and confidence interval (at 95% level) per variety. For
11
each year, the letters indicate significant differences between varieties (LSD method, p < 5%).
12
For Starina and Meiburenac, we considered all the flowers except the terminal ones. For Pink
13
Wonder and Kolima, we considered all the flowers.
Variety
2009, greenhouse
Number Mean
of plants
2010, outdoors
Confidence
Number Mean
interval
of plants
Confidence
interval
Pink Wonder
6
84.8
[78.9 , 90.6]
a
6
83.7
[80.3 , 87.1] a
Kolima
6
73.9
[69.6 , 78.1]
b
6
82.5
[80.1 , 85.0] a
Starina
5
48.9
[46.3 , 51.5]
c
6
46.5
[45.2 , 47.8] b
Meiburenac
5
47.1
[46.5 , 47.8]
c
6
46.2
[44.2 , 48.3] b
14
15
23
16
Table 4. Number of flowers (buds, open or withered flowers) per plant at the first flowering
17
peak. Mean values with the same letters indicate that the corresponding varieties do not differ
18
significantly at p<5%, using non-parametric test on ranks.
Variety
2009, greenhouse
2010, outdoors
Number Mean (standard
Number
Mean (standard
of plants
deviation)
of plants
deviation)
Meiburenac
5
104.5 (30.3)
a
6
212.7 (94.2)
a
Kolima
6
23.7 (2.3)
b
6
32.7 (8.0)
b
Meichim
5
11.6 (4.9)
c
6
23.3 (13.9)
bc
Sweet Promise
6
15.2 (3.1)
c
6
17.2 (5.3)
c
19
24
20
Table 5. Floribundity measurements of 3 rosebushes per variety (2010, outdoors) using the
21
sensory methodology: mean rank according to the quantity of flowers, mean rank according to
22
the relative area occupied by the open flowers and mean score for the flowering level. Mean
23
values with different letters indicate that the corresponding varieties are significantly different
24
at p<5%, using non-parametric tests on ranks.
Variety
Number
Mean rank
Mean score (1 to 9
of
(increasing order from 1 to 12)
scale) for flowering
measures
Quantity
Relative area occupied
of flowers
by the open flowers
level
Meiburenac
48
10.8
10.0
7.8 (1.0)
a
Kolima
48
6.9
7.0
6.7 (1.2)
b
Sweet Promise
48
4.3
4.9
4.8 (2.1)
c
Meichim
48
4.0
4.1
4.4 (2.2)
d
25
25
26
Table 6. Spearman correlations between the 3 sensory measurements on photographs of the
27
plants (Table 5), the relative area occupied by the flowers measured by ImageJ and the
28
number of flowers counted on the real plants on the days when the photographs were taken.
Measurement
Ranking: quantity of flowers
(1)
Ranking: relative area occupied by the open flowers
(2)
Score of the flowering level
(3)
Number of flowers on the real plants
(4)
Relative area occupied by the flowers (ImageJ)
(5)
(1)
(2)
1
0.91 0.88 0.96 0.86
1
(3)
(4)
(5)
0.90 0.88 0.92
1
0.83 0.90
1
0.82
1
29
26
Figure_1
Figure 1
a
b
c
Figure_2
Figure 2
Figure_3
Figure 3
Relative flower
area
No. of flowers
Flower
enhancement
No. of buds
0.124
8.5
0.122
8.3
0.083
8.2
0.032
5.5
5.6
8.0
7.0
5.5
7.1
4.3
5.8
1.9
0.024
5.3
0.021
2.9
0.020
2.8
0.015
6.2
0.004
4.6
0.001
2.8
3.5
8.8
6.3
2.7
6.7
3.2
5.9
6.9
4.5
8.1
2.7
5.6
Figure_4
Figure 4
Figure_5
Figure 5
Figure_6
Figure 6